Korean Job Discussion Forums

[Binch Lover]

Didn't notice Nari coming through since I live in Seoul but this one looks like it could hit us smack bang dead on. Looks like sports day is gonna be cancelled...

http://www.wunderground.com/tropical/tracking/wp200713.html[/url]

[SeoulShakin]

It looks like it's just supposed to be a tropical storm when it hits us, so hopefully it's just some rain we have to deal with. Fingers Crossed.

My vice-principal is doing announcements right now and speaking about how Nari affected the people on Jeju-do and in Cheollanam-do (sp?).

[pest2]

I see varying predictions about its track. Some are saying it'll hit us, others saying it wont... If it doesnt, we'll have clear skies starting Thursday. If it does, the rain will last yet another week. I am really getting sick of clouds and rain.

[Freakstar]

[nobbyken]

Really nice cloudless night in Suwon last night.

Anybody else out for a cycle or walk and notice how bright it was?

[mrsquirrel]

Coriolis in meteorology
This low pressure system over Iceland spins counter-clockwise due to balance between the Coriolis force and the pressure gradient force.
This low pressure system over Iceland spins counter-clockwise due to balance between the Coriolis force and the pressure gradient force.

Perhaps the most important instance of the Coriolis effect is in the large-scale dynamics of the oceans and the atmosphere. In meteorology, it is convenient to use a rotating frame of reference where the Earth is stationary. The fictitious centrifugal and Coriolis forces must then be introduced. The former, however, is cancelled by the non-spherical shape of the earth (see the turntable analogy above). Hence the Coriolis force is the only fictitious force to have a significant impact on calculations.

[edit] Flow around a low-pressure area
Schematic representation of flow around a low-pressure area in the Northern hemisphere. The pressure-gradient force is represented by blue arrows, the Coriolis acceleration (always perpendicular to the velocity) by red arrows
Schematic representation of flow around a low-pressure area in the Northern hemisphere. The pressure-gradient force is represented by blue arrows, the Coriolis acceleration (always perpendicular to the velocity) by red arrows

If a low-pressure area forms in the atmosphere, air will tend to flow in towards it, but will be deflected perpendicular to its velocity by the Coriolis acceleration. A system of equilibrium can then establish itself creating circular movement, or a cyclonic flow.

The force balance is largely between the pressure gradient force acting towards the low-pressure area and the Coriolis force acting away from the center of the low pressure. To get some grip on the size of the effect, consider a high-pressure area at 1020 mbar at a distance of 1000 km from a low at 980 mbar. The pressure gradient is then 0.004 N/m3. Then consider a wind at moderate speed of 50 km/h at a latitude of 30� and an air density of 1.2 kg/m3. This leads to a Coriolis force of 0.0012 N/m3 or about 30% of the pressure gradient. So the Coriolis force is a sizable effect.

Instead of flowing down the gradient, the air tends to flow perpendicular to the air-pressure gradient and forms a cyclonic flow. This is an example of a more general case of geostrophic flow in which air flows along isobars. On a non-rotating planet the air would flow along the straightest possible line, quickly leveling the air pressure. Note that the force balance is thus very different from the case of "inertial circles" (see below) which explains why mid-latitude cyclones are larger by an order of magnitude than inertial circle flow would be.

This pattern of deflection, and the direction of movement, is called Buys-Ballot's law. The pattern of flow is called a cyclone. In the Northern Hemisphere the direction of movement around a low-pressure area is counterclockwise. In the Southern Hemisphere, the direction of movement is clockwise because the rotational dynamics is a mirror image there. However, at high altitudes, outward-spreading air rotates in the opposite direction. [3] Cyclones cannot form on the equator, because in the equatorial region the coriolis parameter is small, and exactly zero on the equator.

[edit] Inertial circles
Schematic representation of inertial circles of air masses in the absence of other forces, calculated for a wind speed of approximately 50 to 70 m/s. Note that the rotation is exactly opposite that normally experienced with air masses in weather systems around depressions.
Schematic representation of inertial circles of air masses in the absence of other forces, calculated for a wind speed of approximately 50 to 70 m/s. Note that the rotation is exactly opposite that normally experienced with air masses in weather systems around depressions.

An air or water mass moving with speed v\, subject only to the Coriolis force travels in a circular trajectory called an 'inertial circle'. Since the force is directed at right angles to the motion of the particle, it will move with a constant speed, and perform a complete circle with frequency f. The magnitude of the Coriolis force also determines the radius of this circle:

R=v/f\,.

On the Earth, a typical mid-latitude value for f is 10−4 s−1; hence for a typical atmospheric speed of 10 m/s the radius is 100 km, with a period of about 14 hours. In the ocean, where a typical speed is closer to 10 cm/s, the radius of an inertial circle is 1 km. These inertial circles are clockwise in the northern hemisphere (where trajectories are bent to the right) and anti-clockwise in the southern hemisphere.

If the rotating system is a parabolic turntable, then f is constant and the trajectories are exact circles. On a rotating planet, f varies with latitude and the paths of particles do not form exact circles. Since the parameter f varies as the sine of the latitude, the radius of the oscillations associated with a given speed are smallest at the poles (latitude = �90�), and increase toward the equator.

[edit] Length scales and the Rossby number

Further information: Rossby number

The time, space and velocity scales are important in determining the importance of the Coriolis effect. Whether rotation is important in a system can be determined by its Rossby number, which is the ratio of the velocity, U, of a system to the product of the Coriolis parameter, f, and the length scale, L, of the motion:

Ro = \frac{U}{fL}.

A small Rossby number signifies a system which is strongly affected by rotation, and a large Rossby number signifies a system in which rotation is unimportant.

An atmospheric system moving at U = 10 m/s occupying a spatial distance of L = 1000 km, has a Rossby number of approximately 0.1. A man playing catch may throw the ball at U = 30 m/s in a garden of length L = 50 m. The Rossby number in this case would be about = 6000. Needless to say, one does not worry about which hemisphere one is in when playing catch in the garden. However, an unguided missile obeys exactly the same physics as a baseball, but may travel far enough and be in the air long enough to notice the effect of Coriolis. Long-range shells in the Northern Hemisphere landed close to, but to the right of, where they were aimed until this was noted. (Those fired in the southern hemisphere landed to the left.)

The Rossby number can also tell us about the bathtub. If the length scale of the tub is about L=1m, and the water moves towards the drain at about 60cm/s, then the Rossby number is about 6 000. Thus, the bathtub is, in terms of scales, much like a game of catch, and rotation is likely to be unimportant.


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[Ya-ta Boy]

[Optimus Prime]

[bassexpander]

Oh well, I'm sick and can't leave the house anyway.

That's why I keep posting on here so much.

[newton kabiddles]

love it, love rain, hope we get it full force

[AylaZ]

Hey, I hadn't seen news etc, was in Jeju for a week. got caught in it pretty full on. River near Motel broke through to road, no power for day. chaos.

[IncognitoHFX]

[bassexpander]

newton, the head on that avatar lady of yours is so small, she looks like she's retarded.

It makes me sad.

[crazy_arcade]

[Alyallen]